Exhaust emission control system

ABSTRACT

An exhaust emission control system for an internal combustion engine having an air injection system in which exhaust system pressure pulsations are used to induce air flow through an air induction valve to the engine exhaust ports to deliver air to the stream of exhaust gases as they are emitted from the combustion chambers.

Unite States Patent [151 3,653,212 Gast et a1. [45] Apr. 4, 1972 [54]EXHAUST EMISSION CONTROL 2,847,820 8/1958 Leach ....60/32 M SYSTEM3,468,124 9/1969 Hraboweckyj ..60/30 R [72] lnventors: Richard A. Gast,Southfield; Harry R.

Mitchell, Bloomfield Hills, both of Mich.

[73] Assignee: General Motors Corporation, Detroit,

Mich.

[22] Filed: Oct. 30, 1970 [21] Appl. No; 85,379

[52] U.S. Cl. ..60/30 R, 60/32 M [51] Int. Cl ..F0ln 3/10 [58] Field ofSearch ..60/30 R, 32 M [56] References Cited UNITED STATES PATENTS2,841,951 7/1958 Whitcomb ..60/32 M FOREIGN PATENTS OR APPLICATIONS1,926,041 1/1970 Germany 60/30 R Primary Examiner-Douglas HartAttorney-Jean L. Carpenter and Arthur N. Krein [5 7] ABSTRACT An exhaustemission control system for an internal combustion engine having an airinjection system in which exhaust system pressure pulsations are used toinduce air flow through an air induction valve to the engine exhaustports to deliver air to the stream of exhaust gases as they are emittedfrom the combustion chambers.

10 Claims, 12 Drawing Figures a I f PATENTEBAPR 4 I972 3,653,212

SHEET 3 OF 3 2200 l/-3 PUISE.S//; REV. I800 D. X

It 600 SPULSES/Z REV. g S 2 3 I 0 I12 I14 [I6 ENGINE RPM FOR MAX.PULSAIR FLOW if aw ENGINE TO Y EXHAUST LENGTH FEET ENGINE To-Y EXHAUSTLENGTH FEET 3 PuLSES/2 REV.

\ S PULSES/Z REV d zzy EXHAUST EMISSION CONTROL SYSTEM During recentyears, increasing emphasis has been placed on reducing the amount ofunburned constituents, such as hydrocarbon and carbon monoxide presentin the exhaust gases emitted from internal combustion engines. One ofthe most effective arrangements devised to accomplish this reduction isthe air injection reactor system. In this system, an engine driven airpump delivers air to the stream of hot exhaust gases as they are emittedfrom the engine combustion chambers. Utilizing the heat of the exhaustgases, the injected air supports additional burning of the exhaust gasesin the engine exhaust passages to reduce the amount of unburnedconstituents in the exhaust gases discharged to the atmosphere.

Other air injection reactor systems have been proposed in which the airpump is replaced by eductors embodied in the cylinder head of theengine, as disclosed, for example, in U.S. Pat. Nos. 3,285,002 and3,335,564 issued on Nov. 15, 1966, and Aug. 15, 1967, respectively, toEugene W. Hines, but these arrangements add significantly to the cost ofthe engine, in fact, probably costing more than the air pump which theyare intended to replace.

Prior to the introduction of the above-identified air injection reactorsystems, it had previously been suggested to introduce air into theexhaust system of an internal combustion engine through speciallyconstructed vibration frequency responsive valves. However, none of thelast mentioned systems delivered the air to the stream of hot exhaustgases as they are emitted from the engine combustion chambers directlyadjacent to the exhaust valves nor were they adequate to inducesufficient flow of air into the exhaust system to reduce the amount ofunburned constituents in the exhaust gases to meet present day emissioncontrol standards.

Accordingly, it is an object of this invention to improve an exhaustemission control system whereby exhaust system pressure pulsations areused to induce sufficient air flow into the exhaust system of aninternal combustion engine to support additional oxidizing or burning ofthe exhaust gases in the engine exhaust passages and thereby reduce theamount of unburned constituents in the exhaust gases to a level belowthe presently forecast emission control standards for internalcombustion engines in motor vehicles.

Another object of this invention is to provide an improved exhaustemission control system whereby, through the proper selection of exhaustsystem length and configuration, sufficient air is induced to flow tothe engine exhaust ports by means of exhaust system pressure pulsations.

These and other objects of the invention are obtained by means of anexhaust emission control system for and internal combustion engine inwhich an engine having an N number of combustion chambers is providedwith a plurality of exhaust conduits, each of which is connected to amaximum of N/2 number of combustion chambers and each exhaust conduit isprovided with passages to direct air toward the combustion chambersexhausting into that exhaust conduit, the passages being connected by anair induction valve to the atmosphere, each of the exhaust conduitsbeing of a predetermined length for a particular range of engineoperating speeds to effect maximum flow of air into the exhaust system.

For a better understanding of the invention, as well as other objectsand further features thereof, reference is had to the following detaileddescription of the invention, to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of an internal combustion engine having anexhaust emission control system in accordance with the invention;

FIG. 2 is an enlarged rear view of the engine of FIG. 1, with partsbroken away, to show the details of the air induction tube of the airinjection reactor of the exhaust emission control system and showingschematically a modified exhaust crossover in the exhaust system of theengine;

FIG. 3 is a top view of an engine similar to that of FIG. 2 with anexhaust Y-connection and a modified exhaust crossover system;

FIG. 4 is a top view of the air induction valve assembly of FIG. 1 withparts broken away to show details of its structure;

FIG. 5 is a sectional view of the air induction valve assembly takenalong line 5--5 of FIG. 4;

FIG. 5a is an enlarged view of a portion of the air induction valveassembly of FIG. 5 showing details of the timing valve arrangement;

FIG. 6 is a schematic illustration of a symmetrical, single exhaustsystem for a V-8 engine;

FIG. 7 is a graph showing optimum exhaust length versus engine speed forthe symmetrical, single exhaust system of FIG. 6;

FIG. 8 is a schematic illustration of an asymmetric, single exhaustsystem for a V-8 engine;

FIG. 9 is a graph showing optimum exhaust length versus engine speed forthe asymmetric, single exhaust system of FIG. 8;

FIG. 10 is a schematic illustration of dual exhaust system with balancepipe for a V-8 engine; and,

FIG. 11 is a graph showing optimum exhaust length to balance pipe versusengine speed for the dual exhaust system of FIG. 10.

Referring now to FIGS. 1, 2 and 3, there is shown, for purposes ofillustration, a V-8 engine 10 which is provided with a carburetor 11 andan air filter 12. The rightand left-hand banks of four cylinders each ofthe engine are provided with right-hand and left-hand exhaust manifoldsl3 and 14, respectively, which are connected to exhaust pipes asdescribed hereinafter. Rightand left-hand air manifolds 15 and 16 areeach provided with a series of air injection tubes 17 extending into therespective exhaust manifolds through which air is in jected into thestream of exhaust gases adjacent to the combustion chamber exhaustvalves 18, as shown in FIG. 2. The air manifolds 15 and 16 are connectedby conduits 21 and 22, respectively, to the discharge outlets of an airinduction valve assembly, generally designated 23, suitably supported onthe engine and, which has its inlet connected to a suitable source ofclean air at atmospheric pressure, such as by connection of hose 24 tothe air filter 12 downstream of the filter element therein, not shown.

In the operation of the air induction valve 23, as seen in FIGS. 3, 4and 5, air flows from hose 24 through inlet 25 of valve casing 26 past aspring 27 biased normally open valve 31 into chamber 28. From thechamber 28, the air flows through a plurality of reed-type check valves32. Reed valves 32 open as the exhaust manifold pressure drops belowatmospheric, as explained in detail hereinafter, to permit air flowthrough the outlets 33 of reed valve covers 34 into conduits 21 and 22,previously described.

In the embodiment of the air induction valve shown, a diaphragm 35actuated control is adapted to close valve 31 and prevent air injectionduring engine deceleration to prevent back-firing. Intake manifoldvacuum is supplied through hose 36 and tube 37 to the chamber 38 abovethe pressure responsive diaphragm 35. During deceleration, the highinduction vacuum in effect pulls diaphragm 35 upwardly against the biasaction of spring 27 to close valve 31. A timing valve 41 in the stem 42gradually balances the pressure between chamber 38 above diaphragm 35and the chamber 43 below diaphragm 35 so that the valve 31 is closedonly for a predetermined interval.

The air induction valve 23, in the embodiment disclosed, includes thevalve casing 26 supporting on opposite sides thereof, valve seat members44, each enclosed by a reed valve cover 34. Each valve seat member 44has a passage 45 in communication with chamber 28 and terminating inoutlet ports 46. As shown, each valve seat member is provided with twosets of opposed outlet ports 46, discharge through which is controlledby the reed valves 32. Each reed valve 32 is secured at one end with itsunsecured end normally seated on the face of the valve seat member 44around the respective outlet port 46 to effectively close the outletport. A reed retainer 47 is secured over the fixed end of each reedvalve and projects over it in a predetermined arc to limit flexing ofits associated reed valve.

The stem 42, which has secured at the reduced end thereof the valve 31,is slideably joumaled in the bottom wall of the valve casing 26 and isnormally biased downward to the position shown in FIG. by spring 27 tounseat valve 31 from valve seat 48. Diaphragm 35 is secured to theannular base portion of stem 42 and is clamped at its outer peripherybetween bottom cover 51 and valve casing 26 to form therewith chambers38 and 43.

Timing valve 41, which is a disc of flexible metal, is provided with aflapper portion formed by an arcuate slot 52 which overlies an annularrecess 53 in the base of stem 42, both the diaphragm 35 and timing valve41 being secured to the stem by retainer 54 fixed thereon. Annularrecess 53 is connected by a bleed groove 55 of predetermined size topassage 56 in the stem in communication with chamber 38. With thisarrangement during engine deceleration, high induction vacuum introducedin chamber 38 will allow pressure in chamber 43 to move diaphragm 35upward to close valve 31. At this time, timing valve 41 is closed, butair can bleed between chambers 38 and 43 through the arcuate slot 52,annular recess 53, bleed groove 55 and passage 56. After a timeinterval, determined by the size of the bleed groove 55, the pressuresin chambers 38 and 43 are sufficiently balanced so that spring 27 willagain lower valve 31.

if, however, before the pressure in chambers 38 and 43 is substantiallybalanced as described above, the engine is suddenly accelerated, thepressure in chamber 38 will rise rapidly to reflect the pressure changein the induction manifold. As this occurs, the flapper portion of timingvalve 41 will open placing chambers 38 and 43 in direct communicationwith each other for rapid balancing of the pressure in these chambers tomaintain valve 31 open by the biasing action of spring 27.

Referring now to the exhaust emission control system of the invention,exhaust system pressure pulsations in the exhaust system of the engineare used to induce air into the exhaust ports of the engine via the airinjection tubes previously described. This technique is advantageousbecause it does not require engine power and because it replaces the airpump of the previously described prior art air injection reactor systemswith high speed check valves which allow air to flow into the exhaustports when the exhaust pressure in the exhaust system fluctuates belowatmospheric pressure. These subambient depressions occur because thepressure waves produced by combustion chamber blowdown reflect from theopen end of the exhaust system as expansion waves. To induce sufficientair for emission control, as required by current and proposed emissioncontrol standards, the exhaust system must be tailored to producecomposite pulsation frequencies which the check valves 32 can followeffectively.

To more clearly understand how air is induced into the exhaust emissioncontrol system of the invention, a theory of operation is set forthherein. Consider, for example, a single cylinder engine operating withan attached exhaust pipe. During engine operation, when the exhaustvalve opens, a pres sure wave pulses from the combustion chamber intothe exhaust port and travels at the speed of sound through the exhaustsystem. The effect of this single exhaust event does not end when thepressure wave passes out the end of the pipe. A wave is reflected backthrough the pipe, and continued reflections will occur until completelyattenuated. Each pressure wave which reaches the open or atmospheric endof the pipe reflects back through the system as an expansion, orrarefication, wave. Similarly, an expansion wave is reflected from theopen end of the pipe as a pressure wave. Pressure and expansion wavesreflect from the closed exhaust port end of the pipe as pressure andexpansion waves, respectively. Thus, several periods of subatmosphericpressure can be generated by reflection from a single exhaust pulse.With vehicle exhaust systems incorporating mufflers and a plurality ofpipes, these effects will occur but the constant pressure boundary whichcreates the expansion waves does not necessarily coincide with thephysical end of the tail-pipe.

With typical engine operation, a second exhaust event will occur beforereflections from the first pressure wave are attenuated completely.Subsequent waves and their reflections soon combine with one another toform a composite wave which is repeated each engine cycle untiloperating conditions are changed. When two or more waves encounter oneanother, the resulting amplitude is the sum of the amplitudes whichwould occur independently in each wave. After the waves have passed oneanother, they are unaffected by the encounter,

As a result of the above effects, the number of subatmosphericdepressions occuring in one single-cylinder engine cycle, that is, twocrankshaft revolutions per engine cycle, is determined by engine speed,the length and shape of the exhaust system and the speed of sounddetermined by properties of the exhaust gases. The magnitude of thedepressions is determined primarily by the pressure level in thecombustion chamber at the instant the exhaust valve opens and theattenuation properties of the exhaust system. Both the magnitude and thenumber of depressions are affected by the exhaust valve opening scheduleas determined by the valve actuating cam profile and by the interactionsof waves produced by successive exhaust pulses. The air-fuel intakesystem of the engine may also generate pressure depressions in theexhaust system because the intake valve opens while the exhaust valve isstill open, referred to as valve overlap. This is of little concern in amulticylinder engine, of the type shown in FIG. 1, because of tailoringof the exhaust system only has been found to produce an effective airinduction system for purposes of exhaust emission control.

Considering now a multi-cylinder engine, of the type most commonly usedin motor vehicles, wherein several cylinders exhaust to a commonmanifold, the effects of the pressure waves are much more complex. Wavesfrom several cylinders travel and reflect through the common exhaustpipe. Each wave maintains its identity independently of the other, butwhere two or more waves are present at the same time, the waves aresuperimposed. As a result of the superimposability, the firing order ofthe cylinders which are manifolded together determine the nature of thecomposite wave produced at any given location within the system.Further, connecting two or more exhaust pipes from the same engineallows the expansion waves from one pipe to reinforce those in theothers at certain conditions. These parameters as well as thosediscussed above which affect the wave from one cylinder, must beconsidered in the design of an effective pulsing air injection systemaccording to the invention.

In order to induce useful air flow rates, engine and exhaust systemcomponents must produce exhaust pressure pulsation frequencies withinthe limitations established by check valve response in the air inductionvalve 23 and which result in depressions of sufficient time duration toallow air to accelerate through the valve. Engine speed and the numberof static pressure depressions occuring in one engine cycle determinethe operating frequency of these check valves. This operating frequency(f) can be determined for the purpose of this disclosure as:

: (r.p.m.) (depressions/cycle) (2 revs/cycie) (6O sec/mini From thisformula, it is apparent that for a given engine speed, the operatingfrequency (1) required of the check valves 34 is directly related to theexhaust wave depressions or pulsations per engine cycle. In order toincrease the effectiveness of the check valves, it is desirable todecrease the frequency and increase the amplitude of these pressurefluctuations, it being understood that the proper check valves are thenselected for operation at this predetermined frequency.

In a multi-cylinder engine consisting of N number of combustionchambers, such as that used in a motor vehicle, the exhaust wave is acomposite wave formed by superimposition of the waves from theindividual cylinders. This can be taken advantage of by the use ofclosely connected exhaust ports, such as that obtained with conventionalexhaust manifolds connecting N/2 combustion chambers, because theexhaust manifold then acts like a plenum controlled by a relatively longexhaust pipe as described hereinafter. Thus, all exhaust ports closelyconnected by an exhaust manifold will experience a pressure depressionat the same time. They can therefore be supplied by a common group ofcheck valves as shown in FIG. 2 to induce air to flow at the same time.

It has been found, however, that if the exhaust ports of more than N/2combustion chambers are closely connected as, for example, if the rightand left exhaust manifolds of a V-8 engine are relatively closelyconnected, the composite pressure pulsations will be of relatively lowamplitude and high frequency. Thus, if these two exhaust manifolds arerelatively closely interconnected as by a conventional exhaust crossoverpassage used for heating the engine air-fuel mixture, useful air flowrates will be induced only at very low engine speeds. It has now beenfound that this pulsation frequency can be reduced and the amplitudegreatly increased by the elimination of such a relatively closeconnection between the exhaust manifolds.

It has also been found that maximum air flow occurs when the exhaustblowdown pulses and their reflections combine in a manner to reinforcethe exhaust system resonant frequency f which is determined by f speedof sound/wave length. For each type of exhaust system, this resonantfrequency is determined by a characteristic wave length which isdependent on physical pipe lengths and which can be designated or tuned"to produce maximum air flow at a desired engine speed. This is essentialbecause maximum induced air flow is required in order to effectivelycombine sufficient air with the hot exhaust gases to reduce emissions tomeet present day emission control standards. If the exhaust system isproperly tuned, sufficiently high air flow rates will be induced for anengine speed range of several hundred revolutions per minute. Thispermits an exhaust system design for a given engine speed that willprovide high air flow rates for the lower half of the designed enginespeed range where emission control is needed the most, it being realizedthat at higher engine speeds the air-fuel ratio and high exhausttemperatures are such as to cause reduced emission with significantlyless induced air flow.

As previously described, an exhaust manifold acts like a plenumcontrolled by a relatively long exhaust pipe. As such, the exhaustmanifold and the exhaust pipe can be tuned by proper selection of theoverall effective length of this portion of the exhaust system fordifferent exhaust system configurations.

It has been found that air flow induction systems, as disclosed herein,are effective with all types of exhaust systems, with best resultsobtained with Y-connected single systems and balance-piped dual systems,the latter system being capable of inducing up to thirty percent higherair flow rates than the former. It has also been found that both of theaforementioned V-8 exhaust systems can be tuned for maximum air flowinduction with predictable numbers of three and five static pressuredepressions for each engine cycle, or two crankshaft revolutions, thispredictability resulting in an accurate formulation of the requiredexhaust lengths for an effective air induction system. Accordingly, onlythese two exhaust systems are illustrated and described in detailhereinafter.

Referring now to FIG. 6, there is illustrated schematically a symmetricsingle exhaust system while FIG. 7 is a graph showing how engine speedsproducing maximum induced air flow rates are correlated with the engineto Y-connection length of the exhaust system, the length referred toincluding the flow length within the exhaust manifold as seen in FIG. 6.As shown, exhaust manifolds 13 and 14 are connected by approximatelyequal length exhaust pipes 61 and 62, respectively, and Y-connector 63to a common muffler 64 and tailpipe 65, The critical tuning length ofeach exhaust system for an engine operating at a predetermined speed isthe flow length of the exhaust manifold and the flow length of itsassociated exhaust pipe up to the Y-connector. In other words, it hasbeen found that the position of the muffler or the length of thetailpipe has no significant effect on induced air flow, if engine toY-connector lengths are selected from the graph shown in F [67 7 ordetermined from the formula to be described hereinafter. In each ofFIGS. 7, 9 and 11 graphs are shown for pressure-wave pulse rates ofthree and five pulses for each engine cycle, but for purposes of thisdisclosure, the five pulse rate is of primary concern in the formulationof effective air induction systems.

It is not always possible to install a completely symmetrical exhaustsystem in a vehicle. Mandatory positioning of structural members anddrive-train components quite often requires severe asymmetry in theexhaust system to prevent interferences. For this reason, there is shownin FIG. 8 an asymmetric single exhaust system in which the exhaustmanifolds l3 and 14 are connected by exhaust pipes 61 and 62a,respectively, of unequal length and by Y-connector 63 to a commonmuffler 64 and tailpipe 65. In this arrangement, if the difference inlength between the two exhaust-pipes is less than two feet, then thedesired effective engine to the Y-connector exhaust length is theaverage exhaust length of the two exhaust systems. If the difference inexhaust pipe lengths is greater than two feet, each bank of the systemwill effect peak flow at different speeds and each bank will haveunequal induced flow rates for a given engine speed.

The conditions for maximum induced air flow rates are plotted by thesolid line in FIG. 9 for exhaust systems with exhaust lengths differingby approximately 4 feet. For comparison, the graph for symmetric systemsare indicated by the dotted curves in this same figure.

Although the Y-connectors are shown as being symmetrical with equalentry angles of approximately 45 into the discharge portion of theconnector, it is to be realized that the configuration of the connectorcan be varied so that the two exhaust conduits can be joined at anydesired suitable angle into the final exhaust conduit discharging intothe muffler 64.

In FIG. 10, there is shown a dual exhaust system with a balance pipe 66interconnecting exhaust pipes 61b and 62b upstream in terms of exhaustflow from the dual mufflers 64. In this arrangement, the lengths of theexhaust system to effect tuning is from the engine to the mid-point ofthe balance pipe for each bank of the exhaust system. In FIG. 11, thereis plotted the graph of the required lengths of the exhaust systemagainst engine speed for a dual exhaust system with balance pipe, thisgraph being shown by the solid line and for comparison purposes, thereis shown by the dotted line the data for a single exhaust system.Although balance pipe 66 is shown as being connected at a right angle toboth exhaust pipes 611; and 6212, these connections can be made at anydesired angle.

Although not shown, it is obvious that a dual exhaust system withoutbalance pipe can also be used to effectively induce air flow for exhaustemission control systems, but it has been found that such a dual systemwithout balance pipe is not as effective and can be relatively noisy ascompared to the described preferred dual exhaust systems with balancepipe.

While graphs similar to those shown in FIGS. 7, 9 and 11 can bedetermined empirically for any given engine and exhaust system, thefollowing equation can be used to determine the length of an exhaustsystem for any V-8 engine with an accuracy of plus or minus 1 foot:

where:

L exhaust length (engine-to-connection of exhaust pipes), ft.; distancefrom most distant combustion chamber to first interconnection betweenexhaust pipes A flow area of exhaust pipe(s), in.

S engine speed for maximum Pulsair flow, revolutions per minute; thisengine speed being selected with regard to the operating speed range atwhich the greatest emission would occur for that engine under normaloperating conditions M number of pipes from exhaust connection tomuffler(s) 1 single Y"-connected systems 2 dual with balance pipe V=volume of exhaust manifold for four cylinders, in.

e the base of the natural system of logarithms; the number lf heating ofthe inducted air-fuel mixture for the engine is desired, the subjectexhaust emission control system can be used by incorporating therein amodified exhaust crossover, as for example, the system as disclosed inFIGS. 2 and 3. In this arrangement, the conventional exhaust crossoverloop from one exhaust manifold to that of the other bank is eliminatedand, instead, as shown, the right-hand bank of the engine has anoutwardly leading exhaust passage 71 which connects with an exhaustcross-passage 72 connected to a secondary exhaust pipe 73 that isconnected back to the right-hand exhaust pipe 61 upstream, in terms ofdirection of the exhaust flow, of the Y-connector 63. This structurepermits hot exhaust gases from the right-hand bank of the engine to flowthrough the exhaust cross-passage 72 to heat the inducted air-fuelmixture as it flows through duct 74 forming part of the intake manifoldfor the engine. Alternately, the second exhaust pipe 73 instead of beingconnected to the exhaust pipe 61, can be connected, not shown, into theair-fuel induction passage of the engine. In determining the requiredtuning length for an engine in the event that no exhaust passages areprovided for heating the air-fuel mixture, then the predicted length fora Y-connected system only should desirably be increased by three-fourthsof a foot from the result obtained from the previously describedequation.

In the above described equation, the tolerance of plus or minus one footallows for differences in exhaust temperature for a given engine designand for the acoustic conductivity of the exhaust interconnections.Including these variables in the above equation would have causedexcessive complications in terms of the benefits to be derived by theirinclusion therein and, therefore, they are not included as variables inthe above described equation to determine a suitable design length forthe effective exhaust length for a given engine.

The subject exhaust emission control system is also suitable for use oneither a six-cylinder engine, not shown, or on a fourcylinder engine,not shown. In the case of a six-cylinder engine, if the engine is a V-6,each bank of cylinders would be isolated from the other bank ofcylinders as in the V-8 engine of FIG. 1. If the engine is an in-linesix-cylinder engine, exhaust manifolding can be on either a 3-3 basis ora 4-2 basis, the 3-3 cylinder arrangement being preferred since it willprovide equal air flow to the two exhaust manifolds and higher inducedair flow rates over a wider speed range than with the 4-2 cylinderarrangement.

What is claimed is:

1. An exhaust emission control system for use on an internal combustionengine having an N number of combustion chambers, said system includinga first exhaust conduit means, a second exhaust conduit means, each ofsaid exhaust conduit means being connected to a maximum of N/2 number ofcombustion chambers, a first passage means and a second passage meansconnected to said first exhaust conduit means and to said second exhaustconduit means, respectively, positioned to direct air into said firstexhaust conduit means and said second exhaust conduit means toward therespective set of said combustion chambers, valve means including checkvalves connected to said first passage means and to said second passagemeans and in communication with the atmosphere and, conduit meansinterconnecting said first exhaust conduit means with said secondexhaust conduit means, the length of at least said first exhaust conduitmeans upstream of said interconnecting conduit means to the most distantcombustion chamber, in terms of the normal flow path of engine exhaust,being greater than 6 feet and less than 14 feet.

2. An exhaust emission control system according to claim 1 wherein bothsaid first exhaust conduit means and said second exhaust conduit meansare greater than 6 feet and less than 14 feet.

3. An exhaust emission control system according to claim 1 wherein saidconduit means interconnecting said first exhaust conduit means with saidsecond exhaust conduit means is a connector having a first intakeportion connected to said first exhaust conduit means, a second intakeportion connected to said second exhaust conduit means and, a commonexhaust discharge portion.

4. An exhaust emission control system according to claim 1 wherein saidconduit means interconnecting said first exhaust conduit means with saidsecond exhaust conduit means is a balance conduit with one end connectedto said first exhaust conduit means and the other end connected to saidsecond exhaust conduit means.

5. An exhaust emission control system according to claim 1 wherein saidfirst exhaust conduit means further includes an exhaust crossoverconduit to the engine for preheating of the induction air-fuel mixturewith a return passage to said first exhaust conduit means.

6. An exhaust emission control system according to claim 2 wherein saidconduit means interconnecting said first exhaust conduit means and saidsecond exhaust conduit means is a balance conduit connected at oppositeends to said first exhaust conduit means and to said second exhaustconduit means and wherein said effective lengths of said first exhaustconduit means and said second exhaust conduit means each include halfthe length of said balance conduit.

7. An exhaust emission control system for use on a V-8 internalcombustion engine having an N number of combustion chambers, said systemincluding a first exhaust conduit means and a second exhaust conduitmeans each of which is connected to N/2 number of combustion chambers,first passage means and second passage means connected to said firstexhaust conduit means and said second exhaust conduit means,respectively, to direct aeriform fluid toward said combustion chambers,valve means connected to said first passage means and said secondpassage means and to a source of aeriform fluid at atmospheric pressure,and conduit means interconnecting said first exhaust conduit means andsaid second exhaust conduit means, the effective length of at least saidfirst exhaust conduit means being equal to length L, plus or minus 1foot according to the equation:

L 12270 0.625(A/M)S .4 3.9 f t M.

where:

L exhaust conduit means length (most distant combustion chamber-to-firstinterconnection of exhaust pipes), ft. A flow area of exhaust pipe (5in. S engine speed for maximum Pulsair flow, rpm M number of pipes fromexhaust connection to muffler l. single Y-connected systems 2. dual withbalance pipe V volume of exhaust manifold for four cylinders, in.

8. An exhaust emission control system according to claim 7 wherein bothsaid first conduit means and said second conduit means are ofapproximately equal lengths.

9. An exhaust emission control system according to claim 7 wherein saidfirst exhaust conduit means further includes an exhaust crossoverconduit to the engine for preheating of the induction air-fuel mixtureto the engine, with a return passage to said first exhaust conduit meansdownstream from said combustion chambers in the direction of normal flowof exhaust gases.

10. An exhaust emission cor trol system according to claim 7 whereinsaid first exhaust conduit means includes a first exhaust manifold forone bank of the V8 engine combustion chambers and said second conduitmeans includes a second exhaust manifold for the other bank ofcombustion chambers.

1. An exhaust emission control system for use on an internal combustionengine having an N number of combustion chambers, said system includinga first exhaust conduit means, a second exhaust conduit means, each ofsaid exhaust conduit means being connected to a maximum of N/2 number ofcombustion chambers, a first passage means and a second passage meansconnected to said first exhaust conduit means and to said second exhaustconduit means, respectively, positioned to direct air into said firstexhaust conduit means and said second exhaust conduit means toward therespective set of said combustion chambers, valve means including checkvalves connected to said first passage means and to said second passagemeans and in communication with the atmosphere and, conduit meansinterconnecting said first exhaust conduit means with said secondexhaust conduit means, the length of at least said first exhaust conduitmeans upstream of said interconnecting conduit means to the most distantcombustion chamber, in terms of the normal flow path of engine exhaust,being greater than 6 feet and less than 14 feet.
 2. An exhaust emissioncontrol system according to claim 1 wherein both said first exhaustconduit means and said second exhaust conduit means are greater than 6feet and less than 14 feet.
 2. - dual with balance pipe V volume ofexhaust manifold for four cylinders, in.3
 3. An exhaust emission controlsystem according to claim 1 wherein said conduit means interconnectingsaid first exhaust conduit means with said second exhaust conduit meansis a connector having a first intake portion connected to said firstexhaust conduit means, a second intake portion connected to said secondexhaust conduit means and, a common exhaust discharge portion.
 4. Anexhaust emission control system according to claim 1 wherein saidconduit means interconnecting said first exhaust conduit means with saidsecond exhaust conduit means is a balance conduit with one end connectedto said first exhaust conduit means and the other end connected to saidsecond exhaust conduit means.
 5. An exhaust emission control systemaccording to claim 1 wherein said first exhaust conduit means furtherincludes an exhaust crossover conduit to the engine for preheating ofthe induction air-fuel mixture with a return passage to said firstexhaust conduit means.
 6. An exhaust emission control system accordingto claim 2 wherein said conduit means interconnecting said first exhaustconduit means and said second exhaust conduit means is a balance conduitconnected at opposite ends to said first exhaust conduit means and tosaid second exhaust conduit means and wherein said effective lengths ofsaid first exhaust conduit means and said second exhaust conduit meanseach include half the length of said balance conduit.
 7. An exhaustemission control system for use on a V-8 internal combustion enginehaving an N number of combustion chambers, said system including a firstexhaust conduit means and a second exhaust conduit Means each of whichis connected to N/2 number of combustion chambers, first passage meansand second passage means connected to said first exhaust conduit meansand said second exhaust conduit means, respectively, to direct aeriformfluid toward said combustion chambers, valve means connected to saidfirst passage means and said second passage means and to a source ofaeriform fluid at atmospheric pressure, and conduit meansinterconnecting said first exhaust conduit means and said second exhaustconduit means, the effective length of at least said first exhaustconduit means being equal to length L, plus or minus 1 foot according tothe equation: where: L exhaust conduit means length (most distantcombustion chamber-to-first interconnection of exhaust pipes), ft. Aflow area of exhaust pipe (s), in.2 S engine speed for maximum Pulsairflow, rpm M number of pipes from exhaust connection to muffler (s)
 8. Anexhaust emission control system according to claim 7 wherein both saidfirst conduit means and said second conduit means are of approximatelyequal lengths.
 9. An exhaust emission control system according to claim7 wherein said first exhaust conduit means further includes an exhaustcrossover conduit to the engine for preheating of the induction air-fuelmixture to the engine, with a return passage to said first exhaustconduit means downstream from said combustion chambers in the directionof normal flow of exhaust gases.
 10. An exhaust emission control systemaccording to claim 7 wherein said first exhaust conduit means includes afirst exhaust manifold for one bank of the V-8 engine combustionchambers and said second conduit means includes a second exhaustmanifold for the other bank of combustion chambers.